The overall goal of the Program Project Grant is to investigate the cellular and molecular biology of lipoprotein and cholesterol metabolism. The major focus of this proposal is to study the structure and function of apolipoproteins (apo-) E and B and the regulation of the genes controlling the biosynthesis of these apolipoproteins. Plasma cholesterol levels are regulated in part by the uptake of plasma lipoproteins via the low density lipoprotein (LDL) receptors on various cells, including hepatocytes. Lipoprotein interaction with the LDL receptors is mediated by apo-E and apo-B on the surface of the lipoproteins. The importance of understanding the details of apo-E and apo-B structure and function is demonstrated by mutations in human genes for these proteins that disrupt normal cholesterol metabolism. Such an understanding is applicable to normal and abnormal metabolism in humans and should enhance our knowledge of hypercholesterolemia and premature coronary artery disease. Our approach will be multidisciplinary, applying the techniques of biochemistry, x-ray crystallography, physical chemistry, cell biology, immunochemistry, ultrastructure, recombinant DNA, animal physiology, and clinical studies. The studies are designed to elucidate the structure of apo-E at the tertiary and quaternary level, to identify precisely the amino acid residues that interact with the LDL receptor, to understand the control of tissue-specific expression of the apo-E gene, and to define the role of apo-E in cholesterol transport in response to cell injury. Studies of apo- B are also designed to define its interaction with the LDL receptor and to understand the factors responsible for apo-B gene regulation and lipoprotein assembly. In addition, the molecular mechanisms involved in the production of the intestinal form of apo-B (B48) will be investigated. The application of basic biochemical, cellular, and molecular approaches will undoubtedly provide important new insights into the roles that these proteins play in lipoprotein transport and cholesterol metabolism and will provide a more complete understanding of their mechanisms of action. The seven research projects within this proposal represent a cohesive, integrated plan to accomplish these goals.